1. Field of the Invention
The present invention relates to a method for forming a micropattern in the technical field of photolithography, more specifically to a method for forming a micropattern capable of dealing with integration and miniaturization of semiconductor devices in recent years.
2. Related Art
In the production of electronic components such as semiconductor devices and liquid crystal devices, photolithographic techniques have been used when a substrate is subjected to an etching treatment, etc. The photolithographic technique includes processes of: forming a coating film (photoresist layer) on a substrate using a so-called radio-sensitive photoresist responsive to the active radiation; then selectively irradiating the photoresist layer with the active radiation for exposure; performing a developing treatment to selectively dissolve and remove the photoresist layer so as to form an image pattern (photoresist pattern), and, with this pattern as a protective layer (mask pattern), forming various patterns including contact patterns such as a hole pattern, and a trench pattern on the substrate.
With a recent growing tendency to integrate and miniaturize semiconductor devices, micro-fabrication in the formation of these patterns has also advanced, and at present ultra-fine processing for a pattern width less than 0.20 μm is demanded. As an active light used in the mask pattern formation, light waves of an excimer laser such as KrF, ArF and F2, as well as short wavelength irradiating lights such as electron beam and EUV (extreme ultraviolet radiation), are utilized. Therefore, research and development of photoresist materials as a mask pattern forming material having properties corresponding to these irradiated lights are performed.
In view of not only the abovementioned photoresist materials, but also pattern formation methods, research, and development of techniques have been performed in order for the pattern micro-fabrication to exceed the resolution limit of conventional photoresist materials.
For example, in a method for forming a micropattern disclosed in Japanese Unexamined Patent Application No. H5-166717, a trimming pattern is formed in a resist for pattern formation that has been coated on a substrate, and after applying a resist for generation of mixing which will mix with the pattern to the entire surface of the substrate, the resist is baked to form a mixing layer from a sidewall to the surface of the resist for pattern formation; followed by removing the non-mixing portion of the resist for generation of mixing so as to attempt to achieve the micro-fabrication of a pattern corresponding to the mixing layer dimension. Furthermore, in a method for forming a micropattern disclosed in Japanese Unexamined Patent Application No. H5-241348, micro-fabrication of a pattern in a certain thickness dimension is attempted by coating a resin which will become insoluble in the presence of an acid on a substrate on which a resist pattern containing an acid-generator was formed; followed by heat-treating to allow the acid to diffuse from the resist to the resin thereby forming a resist of a certain thickness near the interface between the resin and resist pattern; and developing the resist to remove the resinous portion to which the acid has not diffused.
However, since it is difficult to maintain the temperature uniformly within a wafer face in conventionally used heating apparatuses in semiconductor device production according to the methods disclosed in Japanese Unexamined Patent Application Nos. H5-166717 and H5-241348, the thermal dependency of a layer formed on the resist pattern within the wafer face becomes as large as 10 nm/° C., so as to cause a significant problem of pattern dimension unevenness. Furthermore, problems are likely to be caused such as the generation of defects due to a layer formed on the resist pattern and cracks of the layer itself.
On the other hand, a method for micro-fabricating a pattern dimension by fluidizing the resist pattern by the heat-treatment, and so on, has been also known. For example, in Japanese Unexamined Patent Application No. H1-307228, a method is disclosed for forming a micropattern by forming a resist pattern on a substrate, followed by heat-treatment thereof to deform the cross-sectional shape of the resist pattern. Furthermore, in Japanese Unexamined Patent Application No. H4-364021, a method is disclosed for forming a micropattern by forming a resist pattern, followed by heating to fluidize it so as to alter the pattern dimension.
However, in the methods described in Japanese Unexamined Patent Application Nos. H1-307228 and H4-364021, although thermal dependency of the aforementioned resist pattern within a wafer face is as low as about several nm/° C., not only shape deterioration (to become non-rectangular shape) of the resist pattern is observed, but also it is difficult to control the flow level of resist, causing a problem of a difficulty in achieving a uniform narrowing extent of resist pattern within the wafer face.
As a technique to solve these problems in the prior arts, in Japanese Unexamined Patent Application Nos. 2003-107752, 2005-316239 and 2003-142381, the present applicants proposed a coating agent for pattern miniaturization and a technique related to the method for forming a micropattern. With these methods, it has become possible to obtain micropatterns having controllability of the narrowing extent of the resist pattern, an excellent profile, and a property required in semiconductor devices.
In the micropattern forming technique using this coating agent for pattern miniaturization, a photoresist layer is first formed on a substrate, followed by exposing and developing this layer to form a photoresist pattern. Then, after a coating agent for pattern miniaturization is applied over the entire surface of the substrate, the coated substrate is heat-treated so as to widen the photoresist pattern in width through the shrinkage by heat of the coating agent for pattern miniaturization. As a result, the intervals of photoresist pattern are narrowed, and the widths of patterns (various patterns such as hole patterns and trench patterns) defined by intervals of photoresist patterns are also narrowed, thereby obtaining a fine pattern.
Furthermore, Japanese Unexamined Patent Application, First Publication No. 2003-142381 describes a method for forming micropatterns in which the pattern micro-fabrication is repeated several times using the aforementioned coating agent for pattern miniaturization.
However, by way of the coating agent for pattern miniaturization and the method for forming micropatterns described in Japanese Unexamined Patent Application, First Publication Nos. 2003-107752 and 2005-316239, the extent of narrowing of the resist pattern is insufficient. Furthermore, in the method for forming micropatterns described in Japanese Unexamined Patent Application, First Publication No. 2003-142381, not only was it necessary to repeat the same treatment several times in order to obtain a desired dimension of micropatterns, problems of product yield were caused, and also the narrowing extent of the resist pattern is limited.